Method of forming phase change material layer using Ge(II) source, and method of fabrication phase change memory device

ABSTRACT

In one aspect, a method of forming a phase change material layer is provided. The method includes supplying a reaction gas including the composition of Formula 1 into a reaction chamber, supplying a first source which includes Ge(II) into the reaction chamber, and supplying a second source into the reaction chamber. Formula 1 is NR 1 R 2 R 3 , where R 1 , R 2  and R 3  are each independently at least one selected from the group consisting of H, CH 3 , C 2 H 5 , C 3 H 7 , C 4 H 9 , Si(CH 3 ) 3 , NH 2 , NH(CH 3 ), N(CH 3 ) 2 , NH(C 2 H 5 ) and N(C 2 H 5 ) 2 .

PRIORITY CLAIM

A claim of priority is made to Korean Patent Application No. 10-2007-0102585, filed Oct. 11, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

SUMMARY

The present invention generally relates to methods of forming a phase change material layer using a Ge(II) source, and to methods of fabricating a phase change memory device.

Chalcogenide is responsive to temperature conditions to as to be stably transformed between crystalline and amorphous states. The crystalline state has a lower specific resistance than the amorphous state, and this phase change property can be utilized to store data. A phase change random access memory (PRAM) is one example of a memory device which utilizes the phase change characteristics of chalcogenide to store data.

Each unit memory cell of a PRAM generally includes an access device and a phase change resistor which may, for example, be electrically connected between a bit line and a word line of the PRAM. The phase change resistor is a variable resistor and generally includes a phase change material film disposed between a lower electrode and an upper electrode. Typically, the access device is electrically connected to the lower electrode.

FIG. 1 illustrates temperature conditions applied to the phase change resistor during “set” and “reset” programming operations. Set programming refers to the process of placing the phase change resistor in its crystalline state, whereas reset programming refers to placing the phase change resistor in its amorphous state. It should be noted that the terms “crystalline state” and “amorphous state” are relative terms. That is, the phase change resistor need not be fully crystalline in the crystalline state, and the phase change resistor need not be fully amorphous in the amorphous state.

As shown in FIG. 1, set programming entails heating of the phase change material of the phase change resistor at a temperature which falls between a crystallization temperature Tx and a melting point temperature Tm, followed by cooling. Reset programming entails heating the phase change material to the melting point temperature Tm, also followed by cooling. As shown in the figure, the reset programming heat treatment is carried out for a relative short period of time when compared to that of the set programming. Also, the cooling rate in the reset programming may be more rapid than that of the set programming.

The heat treatment itself is achieved by controlling a write current through the phase change resistor to create joule heating conditions which result in temperature profiles that mirror those illustrated in FIG. 1. As a write current flows through the lower electrode and the switching device of the unit memory cell, joule heat is generated at a boundary surface between the lower electrode and the phase change material film. The joule heating induced temperature of the phase change material film is dependent upon the magnitude and duration of the write current.

As mentioned above, the present invention generally relates to methods of forming a phase change material layer using a Ge(II) source and methods of fabricating a phase change memory device.

According to an aspect of the present invention, a method of forming a phase change material layer is provided. The method includes supplying a reaction gas including the composition of Formula 1 into a reaction chamber, supplying a first source which includes Ge(II) into the reaction chamber, and supplying a second source into the reaction chamber. Formula 1 is NR₁R₂R₃, where R₁, R₂ and R₃ are each independently at least one selected from the group consisting of H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) and N(C₂H₅)₂.

According to another aspect of the present invention, a method of forming a phase change material layer is provided. The method include supplying a first source including Ge(II) into a reaction chamber, and supplying a second source into the reaction chamber.

According to still another aspect of the present invention, a method of fabricating a phase change memory device is provided. The method includes loading a substrate including a lower electrode in a reaction chamber, forming a Ge-containing phase change material layer on the lower electrode by supplying a reaction gas including the composition of Formula 1, a first source including Ge(II), and a second source into the reaction chamber in which the substrate is loaded, and forming an upper electrode on the phase change material layer. Formula 1 is NR₁R₂R₃, where R₁, R₂ and R₃ are each independently at least one selected from the group consisting of H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) and N(C₂H₅)₂.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present invention will become readily apparent from the detailed description that follows, with reference to the accompanying drawings, in which:

FIG. 1 is a graph illustrating a method of performing a set or reset programming for a phase change resistor;

FIG. 2 is a flow chart of a method of forming a Ge-containing phase change material layer according to an embodiment of the present invention;

FIG. 3 is a gas pulsing diagram for use in describing the formation of a Ge—Sb—Te layer using chemical vapor deposition according to an embodiment of the present invention;

FIG. 4 is a gas pulsing diagram for use in describing the formation of a Ge—Sb—Te layer using atomic layer deposition according to an embodiment of the present invention;

FIGS. 5A and 5B are cross-sectional views of phase change memory devices prepared according to a method of fabricating a phase change memory device according to an embodiment of the present invention;

FIGS. 6A, 6B and 6C are cross-sectional views of phase change memory devices prepared according to a method of fabricating a phase change memory device according to another embodiment of the present invention;

FIGS. 7A and 7B are photo images illustrating a phase change material layer formed according to an Experimental Example 2;

FIGS. 8A and 8B are photos illustrating a phase change material layer formed according to an Experimental Example 3; and

FIGS. 9A and 9B are photos illustrating a phase change material layer formed according to an Experimental Example 4.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided to present a thorough and complete disclosure, and to fully convey concepts of the invention to those skilled in the art. In the drawings, the relative thicknesses of layers and regions are not necessarily drawn to scale and are exaggerated for clarity. To avoid redundancy in the disclosure, like reference numerals denote the same or similar elements throughout the drawings.

FIG. 2 is a flow chart illustrating a method of forming a phase change material layer according to an embodiment of the present invention.

Referring to FIG. 2, a substrate is loaded into a reaction chamber (S10). The substrate may include a semiconductor material or film at a surface thereof. Examples of the semiconductor material or film include Si and/or SiC. In addition, or alternatively, the substrate may include a dielectric and/or conductive material or film at a surface thereof. Examples of the dielectric material or film include silicon oxide, titanium oxide, aluminum oxide (Al₂O₃), zirconium oxide, and/or hafnium oxide. Examples of the conductive material or film include Ti, TiN, Al, Ta, TaN, and/or TiAlN.

The reaction chamber may, for example, be a cold wall type reaction chamber or a hot wall type reaction chamber. Generally, a cold wall type reaction chamber is capable of processing a single substrate at a time, and includes a substrate stage having heating wires and a shower head located on the substrate stage. On the other hand, the hot wall type reaction chamber includes heating wires in a wall thereof, such that multiple substrates can be vertically stacked within the chamber and batched processed at the same time. In any event, the embodiment is not limited to any particular type of reaction chamber.

Referring again to the example of FIG. 2, a reaction gas which includes a composition represented by Formula 1 is supplied in to the reaction chamber (S20). NR₁R₂R₃  Formula 1 wherein R₁, R₂ and R₃ are each independently H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) or N(C₂H₅)₂.

In the preceding paragraph and throughout this disclosure, the word “independently” means that any two or more of R₁, R₂ and R₃ can be the same as each other, or R₁, R₂ and R₃ can all be different from each other.

The representation of Formula 1 includes non-ring systems, and ring systems in which two or more of R₁, R₂ and R₃ are bonded to each other. In other words, according to Formula 1, two or more of R₁, R₂ and R₃ may or may not be bonded to each other.

As one particular example, the reaction gas is an NH₂ gas. Other specific examples of the reaction gas any one or more of ammonia, primary amine and hydrazine.

Referring again to FIG. 2, a Ge(II) source is supplied as a first source into the reaction chamber (S30). Here, “II” denotes an oxidation state of the Ge is +2. The Ge(II) can be supplied before and/or after and/or at the same time the reaction gas is supplied into the reaction chamber.

The Ge(II) source may, for example, be supplied together with a carrier gas. Examples of the carrier gas include an inert gas such as argon (Ar), helium (He) or nitrogen (N₂). As another example, the Ge(II) source may be supplied into the reacton chamber by being dissolved in a solvent and rapidly gasified in a gasifier.

Examples of Ge(II) source include an amide ligand, a phosphanido ligand, an alkoxide ligand or a thiolate ligand.

In the case where the Ge(II) source includes an amide ligand and/or a phosphanido ligand, the Ge(II) source may include a composition represented by Formula 2 below: R₁R₂X₁—Ge—X₂R₃R₄  Formula 2 wherein X₁ and X₂ are each independently at least one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently at least one (i.e., one or a combination of two or more) selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, wherein X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₅R₆, where R₅ and R₆ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), and (n) SiR₇R₈R₉, where R₇, R₈ and R₉ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

The representation of Formula 2 includes non-ring systems, and ring-systems in which two or more of R₁, R₂, R₃ and R₄ are bonded to each other. In other words, according to Formula 2, two or more of R₁, R₂, R₃ and R₄ may or may not be bonded to each other.

In the case where the Ge(II) source includes an alkoxide ligand and/or a thiolate ligand, the Ge(II) source may include a composition represented by Formula 3 below: R₁Y₁—Ge—Y₂R₂  Formula 3 wherein Y₁ and Y₂ are each independently at least one of O and S, and wherein R₁ and R₂ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₃R₄, where R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), and (n) SiR₅R₆R₇, where R₅, R₆ and R₇ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

The representation of Formula 2 includes non-ring systems, and ring systems in which R₁ and R₂ are bonded to each other. In other words, according to Formula 3, R₁ and R₂ may or may not be bonded to each other.

In the case where the Ge(II) source includes one of the amide ligand and the phosphanido ligand; and one of the alkoxide ligand and the thiolate ligand, the Ge(II) may include a composition represented by Formula 4 below: R₁R₂X—Ge—YR₃  Formula 4 wherein X is at least one of N and P, wherein Y is at least one of O and S, and wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (g) a C₂-C₁₃ acetylenic group, (h) an allenic group (CHCCH₂), (i) a cyano group (CN), (j) a NCX group, where X is O, S, Se or Te, (k) an azide ligand (N₃), (l) an amide ligand (NR₄R₅, where R₄ and R₅ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), and (m) SiR₆R₇R₈, where R₆, R₇ and R₈ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

The representation of Formula 4 includes non-ring systems, and ring systems in which two or more of R₁, R₂ and R₃ are bonded to each other. In other words, according to Formula 4, two or more of R₁, R₂ and R₃ may or may not be bonded to each other.

Examples of Ge(II) source compositions represented by Formula 2 are presented below as Formulae 5 to 11:

wherein X₁ and X₂ are each independently N or P, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently N or P, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently N or P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently N or P, wherein Y₁ and Y₂ are each independently O or S, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently N or P, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉ and R₁₀ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently N or P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group; and

wherein X₁ and X₂ are each independently N or P, wherein Y₁ and Y₂ are each independently O or S, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.

Examples of Ge(II) source compositions represented by Formula 3 are presented below as Formulae 12 to 16:

wherein Y₁ and Y₂ are each independently O or S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

-   -   wherein Y₁ and Y₂ are each independently O or S, and wherein R₁         and R₂ are each independently one selected from the group         consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂         olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

-   -   wherein Y₁, Y₂, Y₃ and Y₄ are each independently O or S, and         wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one         selected from the group consisting of a hydrogen atom, a C₁-C₁₀         alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group         and an allenic group;

wherein X₁ and X₂ are each independently N or P, wherein Y₁ and Y₂ are each independently O or S, and wherein R₁, R₂, R₃ and R₄ are each independently selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group; and

wherein Y₁, Y₂, Y₃ and Y₄ are each independently O or S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.

AN example of a Ge(II) source composition represented by Formula 4 is presented below as Formula 17:

wherein X is N or P, wherein Y is O or S, and wherein R₁, R₂ and R₃ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.

When compared to a Ge(IV) source, the Ge(II) sources described above exhibit fewer ligands and a weaker covalent bond property between the Ge and the ligands. According, steric hindrance caused by ligands is relatively weak in the Ge(II) source. Even when the number of ligands of the Ge(II) source and Ge(IV) source is the same, a dative bond among the Ge-ligand bonds of the Ge(II) source may be relatively easily disconnected by heat of the reaction chamber, and thus the Ge (II) source is transformed to a structure with low steric hindrance due to the reduced number of the ligands linked to Ge. Accordingly, the Ge(II) source exhibits improved reactivity when compared to the Ge(IV) source, and thus a temperature required to form the phase change material layer can be reduced.

In particular, for example, the Ge(II) source represented by Formulae 5, 6, 12, 13 and 17 has two atoms linked to Ge, and thus steric hindrance is relatively low. The Ge(II) source represented by Formulae 7, 8, 9 and 14 has four atoms linked to Ge, but the steric hindrance is still relatively low since the top and bottom of the Ge are sterically opened since two ligands of both sides of Ge are almost in the same plane. The Ge(II) source represented by Formulae 10, 11, 15 and 16 also has four atoms linked to Ge, but the steric hindrance is also relatively low since the Ge(II) source is transformed to a structure having two atoms linked to Ge because a dative bond among the Ge-ligand bonds is easily disconnected by heat of the reaction chamber as shown in Reaction Schemes 1 to 4.

In Reaction Scheme 1, X₁, X₂, X₃ and X₄ are each independently N or P, and R₁, R₂, R₃, R₄, R₅ and R₆ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

In Reaction Scheme 2, X₁ and X₂ are each independently N or P, Y₁ and Y₂ are each independently O or S, and R₁, R₂, R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

In Reaction Scheme 3, X₁ and X₂ are each independently N or P, Y₁ and Y₂ are each independently O or S, and R₁, R₂, R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

In Reaction Scheme 4, Y₁, Y₂, Y₃ and Y₄ are each independently O or S, and R₁ and R₂ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

Returning once again to FIG. 2, a second source is supplied into the reaction chamber (S40). The second source may be supplied before or after the reaction gas and/or the Ge(II) source is supplied, or simultaneously with the reaction gas and the Ge(II) source. As a result, a Ge-containing phase change material layer is formed on the substrate (S50).

The second source may also be supplied into the reaction chamber with a carrier gas. Examples of the carrier gas include an inert gas such as argon (Ar), helium (He) or nitrogen (N₂). As an alternative example, the second source may be supplied into the reaction chamber by being dissolved in a solvent and rapidly gasified in a gasifier.

Examples of the second source include one or more of a Te source, a Sb source, a Bi source, an As source, a Sn source, an O source, an Au source, a Pd source, a Se source, a Ti source and a S source. The resultant Ge-containing phase change material layer may, for example, be formed as a Ge—Sb—Te layer, Ge—Bi—Te layer, Ge—Sb layer, Ge—Te—As layer, Ge—Te—Sn layer, Ge—Te layer, Ge—Te—Sn—O layer, Ge—Te—Sn—Au layer, Ge—Te—Sn—Pd layer, Ge—Te—Se layer, Ge—Te—Ti layer, (Ge, Sn)—Sb—Te layer, Ge—Sb—(Se, Te) layer or Ge—Sb—Te—S layer. The Ge-containing phase change material layer may also include one or more impurities such as N, O, Bi, Sn, B, Si or a combination thereof.

For example, when a Te source and/or a Sb source is supplied as the second source, the Ge-containing phase change material layer formed on the substrate may be Ge—Sb—Te layer, Ge—Te layer or Ge—Sb layer. Specific examples of the Te source include Te(CH₃)₂, Te(C₂H₅)₂, Te(n-C₃H₇)₂, Te(i-C₃H₇)₂, Te(t-C₄H₉)₂, Te(i-C₄H₉)₂, Te(CH═CH₂)₂, Te(CH₂CH═CH₂)₂, or Te[N(Si(CH₃)₃)₂]₂. Specific examples of the Sb source include Sb(CH₃)₃, Sb(C₂H₅)₃, Sb(i-C₃H₇)₃, Sb(n-C₃H₇)₃, Sb(i-C₄H₉)₃, Sb(t-C₄H₉)₃, Sb(N(CH₃)₂)₃, Sb(N(CH₃)(C₂H₅))₃, Sb(N(C₂H₅)₂)₃, Sb(N(i-C₃H₇)₂)₃ or Sb[N(Si(CH₃)₃)₂]₃.

The Ge(II) source may react with the reaction gas to form a Ge(II) intermediate in which ligands neighboring the Ge are substituted by the reaction gas. The Ge(II) intermediate may include two NR₁R₂ ligands, wherein R₁ and R₂ are each independently H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) or N(C₂H₅)₂ around Ge. Here, since reactivity between the Ge(II) source and the reaction gas is improved when compared to the reactivity between the Ge(IV) source and the reaction gas, the reaction temperature may be reduced. For example, the Ge(II) source represented by Formula 5 reacts with ammonia to form a Ge(II) intermediate as shown in Reaction Scheme 5 below.

In Reaction Scheme 5, X₁ and X₂ are each independently N or P, and R₁, R₂, R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group.

The Ge(II) intermediate may react with the second source to form a Ge-containing phase change material layer. For example, the Ge(II) intermediate prepared according to Reaction Scheme 5 reacts with a Te source to form a phase change material layer as shown in Reaction Scheme 6 below.

In Reaction Scheme 6, R′ is CH(CH₃)₂.

The Ge(II) intermediate is highly reactive with the second source. Further, similar to the Ge(II) source, the Ge(II) intermediate exhibits low steric hindrance by ligands. As a result, the reaction temperature may be further reduced, and the deposition temperature of the Ge-containing phase change material layer may be reduced. For example, the deposition temperature of the Ge-containing phase change material layer may be less than 300° C., and further, may be 200° C. or less. The grain size of a phase change material layer deposited at such a low temperature is smaller than that of a phase change material layer deposited at a higher temperature. A smaller grain size improves step coverage, which allows a conformal phase change material layer to be formed on the side wall of a contact hole or trench without blocking the hole or trench inlet, thereby avoid the formation of voids within the hole or trench.

The Ge-containing phase change material layer may, for example, be formed using chemical vapor deposition (CVD) or atomic layer deposition (ALD).

FIG. 3 is an example of a gas pulsing diagram in the case where a Ge—Sb—Te layer is formed using chemical vapor deposition.

Referring to FIG. 3, a Ge(II) source, a Sb source and a Te source are simultaneously supplied into a reaction chamber while a carrier gas and a reaction gas are supplied into the reaction chamber. The first reaction gas may be NR₁R₂R₃, wherein R₁, R₂ and R₃ are each independently H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) or N(C₂H₅)₂. As particular examples, the reaction gas may be ammonia, primary amine or hydrazine. The carrier gas may, for example, be an inert gas such as argon (Ar), helium (He) or nitrogen (N₂). The Ge(II) source may be a Ge(II) source as previous described, and may include, for example, an amide ligand, a phosphanido ligand, an alkoxide ligand or a thiolate ligand. The Ge(II) source may react with the reaction gas to form a Ge(II) intermediate in which ligands neighboring Ge are substituted with ligands associated with the reaction gas, and the Ge(II) intermediate may react with the Te source to form GeTe. In addition, the Te source reacts with the Sb source to form Sb₂Te₃. The GeTe and the Sb₂Te₃ can form a Ge—Sb—Te layer having Ge₂Sb₂Te₅ composition. Here, since reactivity between the Ge(II) source and the reaction gas and reactivity between the Ge(II) intermediate and the Te source are improved, a temperature required to deposit GeTe may be reduced. Each of the Ge(II) source, the Sb source and the Te source may be injected at 10 to 1000 sccm for 1 to 1000 seconds. The time for injecting the Ge(II) source, the Sb source and the Te source into the reaction chamber may be defined as deposition time.

FIG. 4 is an example of a gas pulsing diagram in the case where a Ge—Sb—Te layer is formed using atomic layer deposition.

Referring to FIG. 4, a Ge(II) source and a Te source are injected to a reaction chamber while a first carrier gas and a first reaction gas are supplied to the reaction chamber for time T1 to form a Ge—Te layer (first operation). The first reaction gas may be NR₁R₂R₃, wherein R₁, R₂ and R₃ are each independently H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) or N(C₂H₅)₂. As particular examples, the reaction gas may be ammonia, primary amine or hydrazine. The first carrier gas may, for example, include an inert gas such as argon (Ar), helium (He) or nitrogen (N₂). The Ge(II) source may include a Ge(II) source as described previously, and may include amide ligand, a phosphanido ligand, an alkoxide ligand or a thiolate ligand. The Ge(II) source may react with the first reaction gas to form a Ge(II) intermediate in which ligands neighboring Ge are substituted with ligands associated with the reaction gas, and the Ge(II) intermediate may react with the Te source to form GeTe. Here, since reactivity between the Ge(II) source and the first reaction gas and reactivity between the Ge(II) intermediate and the Te source are improved, a temperature required to deposit GeTe may be reduced.

Then, physically adsorbed Ge(II) source and Te source; and unreacted Ge(II) source and Te source are removed by supplying the first carrier gas and the first reaction gas to the reaction chamber while the supply of the sources is suspended for time T2 (second operation).

A Sb source and a Te source are injected to the reaction chamber while supplying a second carrier and a second reaction gas to the reaction chamber for time T3 to form a Sb—Te layer, for example, a Sb₂Te₃ layer (third operation). The second reaction gas may independently include hydrogen (H₂), oxygen (O₂), ozone (O₃), water vapor (H₂O), silane (SiH₄), diborane (B₂H₆), hydrazine (N₂H₄), primary amine or ammonia (NH₃), and the second carrier gas may independently include an inert gas such as argon (Ar), helium (He) or nitrogen (N₂).

Physically adsorbed Sb source and Te source, and unreacted Sb source and Te source are removed by supplying the second carrier gas and the second reaction gas to the reaction chamber while the supply of the sources is suspended for time T4 (fourth operation).

A unit cycle including the first to fourth operations (T1˜T4) may be repeated to form a Ge—Sb—Te layer, for example, a Ge—Sb—Te layer having Ge₂Sb₂Te₅ composition. Each of the Ge(II) source, the Sb source and the Te source may be injected at 10 to 1000 sccm for 0.1 to 60 seconds.

FIGS. 5A and 5B are cross-sectional views of phase change memory devices prepared according to a method of fabricating a phase change memory device according to an embodiment of the present invention.

Referring to FIG. 5A, an isolation layer (not shown) is formed on a substrate 100 to define an active region. A gate insulating layer 105 and a gate conductive layer are sequentially stacked on the active region, and the gate conductive layer 110 and the gate insulating layer 105 are etched to form a gate electrode 110. Impurities are doped on the substrate 100 to a low concentration using the gate electrode 110 as a mask to form a low concentration impurity region 101 a neighboring the gate electrode 110 in the substrate 100.

A gate spacer insulating layer is stacked on the substrate 100 on which the low concentration impurity region 101 a is formed, and the gate spacer insulating layer is anisotropically etched to form a gate spacer 115 on the side wall of the gate electrode 110. Then, impurities are doped on the substrate 100 to a high concentration using the gate electrode 110 and the gate spacer 115 as masks to form a high concentration impurity region 101 b neighboring the gate spacer 115 in the substrate 100.

The low concentration impurity region 101 a and the high concentration impurity region 101 b form source/drain regions. The low concentration impurity region 101 a and the high concentration impurity region 101 b of one end of the gate electrode 110 form a source region 102, and the low concentration impurity region 101 a and the high concentration impurity region 101 b of the other end of the gate electrode 110 form a drain region 103. The gate electrode 110, the source region 102 and the drain region 103 constitute a MOS transistor which functions as an access device. However, the access device is not limited to the MOS transistor, and may instead be a diode or a bipolar transistor.

A first interlayer insulating layer 120 is formed on the substrate 100 on which the source/drain regions 102 and 103 are formed, and a contact plug 125 passing through the first interlayer insulating layer 120 and connected to the drain region 103 is formed within the first interlayer insulating layer 120. The contact plug 125 may, for example, be formed of a tungsten layer.

A lower electrode 135 covering the contact plug 125 is formed on the contact plug 125. The lower electrode 135 may, for example, be formed of a titanium nitride layer (TiN), a titanium aluminum nitride layer (TiAlN), a tantalum nitride layer (TaN), a tungsten nitride layer (WN), a molybdenum nitride layer (MoN), a niobium nitride layer (NbN), a titanium silicon nitride layer (TiSiN), a titanium boron nitride layer (TiBN), a zirconium silicon nitride layer (ZrSiN), a tungsten silicon nitride layer (WSiN), a tungsten boron nitride layer (WBN), a zirconium aluminum nitride layer (ZrAlN), a molybdenum aluminum nitride layer (MoAlN), a tantalum silicon nitride layer (TaSiN), a tantalum aluminum nitride layer (TaAlN), a titanium tungsten layer (TiW), a titanium aluminum layer (TiAl), a titanium oxynitride layer (TiON), a titanium aluminum oxynitride layer (TiAlON), a tungsten oxynitride layer (WON) or a tantalum oxynitride layer (TaON).

A mold insulating layer 140 is formed on the lower electrode 135, and a via hole 140 a which exposes a part of the lower electrode 135 is formed within the mold insulating layer 140. A hole spacer insulating layer is formed on the substrate on which the via hole 140 a is formed, and the hole spacer insulating layer is anisotropically etched to expose the lower electrode 135 in the via hole 140 a. Thus, a hole spacer 145 is formed on the side wall of the via hole 140 a. Accordingly, an effective diameter of the via hole 140 a may be less than a resolution limit of lithography due to the hole spacer 145.

Then, a phase change material layer 150 is formed on the substrate on which the via hole 140 a is formed. The phase change material layer 150 may be a Ge-containing phase change material layer, and formed using the method of FIG. 2. Thus, the deposition temperature of the phase change material layer 150 may be reduced to less than 300° C. Furthermore, the deposition temperature of the phase change material layer 150 may be reduced to 200° C. The phase change material layer 150 deposited at such as low temperature has less grain size than a phase change material layer deposited at a high temperature. Thus, the phase change material layer 150 can fill the via hole 140 a without voids even when the effective diameter of the via hole 140 a is extremely small.

Referring to FIG. 5B, a phase change material pattern 151 is formed by planarizing the phase change material layer 150. An upper electrode 160 is formed on the phase change material pattern 151. The phase change material layer 150 may be planarized using etch back or chemical mechanical polishing (CMP). As a result, a phase change resistor including the lower electrode 135, the upper electrode 160 and the phase change material pattern 151 interposed between the lower electrode 135 and the upper electrode is formed.

FIGS. 6A, 6B and 6C are cross-sectional views of phase change memory devices prepared according to a method of fabricating a phase change memory device according to another embodiment of the present invention. The method of FIGS. 6A˜6C is similar to that of FIGS. 5A and 5B, and accordingly, to avoid redundancy in the description, a discussion of like aspects between the two methods is omitted below.

Referring to FIG. 6A, a mold insulating layer 140 is formed on the lower electrode 135, and a via hole 140 a which exposes a part of the lower electrode 135 is formed within the mold insulating layer 140. A phase change material layer 152 is formed in the via hole 140 a. The phase change material layer 152 does not fully fill the via hole 140 a, but is formed to conformally cover the side wall of the via hole 140 a. The phase change material layer 152 may be a Ge-containing phase change material layer, and formed using the method of FIG. 2. Thus, the deposition temperature of the phase change material layer 152 may be reduced to less than 300° C. Furthermore, the deposition temperature of the phase change material layer 152 may be reduced to 200° C. The phase change material layer 152 deposited at such as low temperature has less grain size than a phase change material layer deposited at a high temperature. Thus, the phase change material layer 152 can conformally cover the side wall of the via hole 140 a without blocking the upper portion of the via hole 140 a.

Referring to FIG. 6B, the phase change material layer 152 is anisotropically etched until the lower electrode 135 is exposed to form a phase change material spacer 153 on the side wall of the via hole 140 a and to expose the upper surface of the mold insulating layer 140. A buffer insulating layer 155 is formed on the exposed lower electrode 135 and the mold insulating layer 140. The buffer insulating layer 155 is formed to fill the via hole 140 a. In the via hole 140 a, the side wall of the buffer insulating layer 155 is covered by the phase change material spacer 153.

The substrate on which the buffer insulating layer 155 is formed is planarized to expose the upper surface of the phase change material spacer 153. For example, the substrate may be planarized to the dashed line shown in FIG. 6B.

Referring to FIG. 6C, an upper electrode 160 is formed on the phase change material spacer 153, the upper surface of which is exposed. Thus, a phase change resistor including the lower electrode 135, the upper electrode 160 and the phase change material spacer 153 interposed between the lower electrode 135 and the upper electrode 160 is formed. The contact area between the phase change material spacer 153 and the lower electrode 135 may be reduced when compared to the phase change material pattern described with reference to FIG. 5B. Accordingly, an effective current density of a writing current applied to the phase change material spacer 153 may further be increased.

Described next are a number of Experimental Examples (1˜13) and Comparative Examples (1˜2).

Experimental Example 1

A substrate was loaded in a reaction chamber. Ar as a carrier gas was supplied into the reaction chamber at 500 sccm and NH₃ as a reaction gas was supplied into the reaction chamber at 100 sccm. A Ge(II) source represented by Formula 18 below was supplied into the reaction chamber at 100 sccm. Simultanesouly, Te(CH(CH₃)₂)₂ was supplied into the reaction chamber at 100 sccm to form a GeTe layer on the substrate. The supply of the Ge(II) source and the Te(CH(CH₃)₂)₂ was performed for 900 seconds. The temperature of a heater of the reaction chamber was set to 320° C.

Experimental Example 2

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 1, except that the temperature of a heater of the reaction chamber was set to 280° C.

Experimental Example 3

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 1, except that the temperature of a heater of the reaction chamber was set to 240° C.

Experimental Example 4

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 1, except that the temperature of a heater of the reaction chamber was set to 200° C.

Experimental Example 5

A substrate was loaded in a reaction chamber. Ar as a carrier gas was supplied into the reaction chamber at 500 sccm and NH₃ as a reaction gas was supplied into the reaction chamber at 100 sccm. A Ge(II) source represented by Formula 19 below was supplied into the reaction chamber at 100 sccm. Simultanesouly, Te(CH(CH₃)₂)₂ was supplied into the reaction chamber at 100 sccm to form a GeTe layer on the substrate. The supply of the Ge(II) source and the Te(CH(CH₃)₂)₂ was performed for 900 seconds. The temperature of a heater of the reaction chamber was set to 320° C.

Experimental Example 6

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 5, except that the temperature of a heater of the reaction chamber was set to 280° C.

Experimental Example 7

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 5, except that the temperature of a heater of the reaction chamber was set to 240° C.

Experimental Example 8

A substrate was loaded in a reaction chamber. Ar as a carrier gas was supplied into the reaction chamber at 500 sccm and H₂ as a reaction gas was supplied into the reaction chamber at 100 sccm. A Ge(II) source represented by Formula 18 was supplied into the reaction chamber at 100 sccm. Simultanesouly, Te(CH(CH₃)₂)₂ was supplied into the reaction chamber at 100 sccm to form a GeTe layer on the substrate. The supply of the Ge(II) source and the Te(CH(CH₃)₂)₂ was performed for 900 seconds. The temperature of a heater of the reaction chamber was set to 320° C.

Experimental Example 9

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 8, except that the temperature of a heater of the reaction chamber was set to 280° C.

Experimental Example 10

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 8, except that the temperature of a heater of the reaction chamber was set to 240° C.

Experimental Example 11

A substrate was loaded in a reaction chamber. Ar as a carrier gas was supplied into the reaction chamber at 500 sccm and H₂ as a reaction gas was supplied into the reaction chamber at 100 sccm. A Ge(II) source represented by Formula 19 was supplied into the reaction chamber at 100 sccm. Simultanesouly, Te(CH(CH₃)₂)₂ was supplied into the reaction chamber at 100 sccm to form a GeTe layer on the substrate. The supply of the Ge(II) source and the Te(CH(CH₃)₂)₂ was performed for 900 seconds. The temperature of a heater of the reaction chamber was set to 320° C.

Experimental Example 12

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 11, except that the temperature of a heater of the reaction chamber was set to 280° C.

Experimental Example 13

A GeTe layer was formed on the substrate in the same manner as in Experimental Example 11, except that the temperature of a heater of the reaction chamber was set to 240° C.

Comparative Example 1

A substrate was loaded in a reaction chamber. Ar as a carrier gas was supplied into the reaction chamber at 500 sccm and NH₃ as a reaction gas was supplied into the reaction chamber at 100 sccm. Ge(N(CH₃)₂)₄ as a Ge(IV) source was supplied into the reaction chamber at 100 sccm. Simultanesouly, Te(CH(CH₃)₂)₂ was supplied into the reaction chamber at 100 sccm to form a GeTe layer on the substrate. The supply of the Ge(IV) source and the Te(CH(CH₃)₂)₂ was performed for 900 seconds. The temperature of a heater of the reaction chamber was set to 320° C.

Comparative Example 2

A GeTe layer was formed on the substrate in the same manner as in Comparative Example 1, except that the temperature of a heater of the reaction chamber was set to 280° C.

Experimental conditions of Experimental Examples 1 to 13, and Comparative Examples 1 and 2, and deposition rates of the resultant GeTe layers are shown in Table 1 below.

TABLE 1 Heater Deposition temperature rate of in reaction Sb₂Te₃ Reaction chamber layer Ge source gas (° C.) (Å/min) Experimental Ge(II) NH₃ 320 12 Example 1 source of Experimental Formula 18 280 10 Example 2 Experimental 240 7 Example 3 Experimental 200 3 Example 4 Experimental Ge(II) 320 8 Example 5 source of Experimental Formula 19 280 4 Example 6 Experimental 240 2 Example 7 Comparative Ge(IV) 320 Deposited Example 1 source Comparative Ge(N(CH₃)₂)₄ 280 Not deposited Example 2 Experimental Ge(II) H₂ 320 4 Example 8 source of Experimental Formula 18 280 0.7 Example 9 Experimental 240 0.1 Example 10 Experimental Ge(II) 320 3 Example 11 source of Experimental Formula 19 280 0.8 Example 12 Experimental 240 0.1 Example 13

Referring to Table 1, when the reaction gas was NH₃, a phase change material layer was formed at a temperature less than 300° C., that is, at 280° C., at 240° C., and even at 200° C. using the Ge(II) source of Formula 18. However, when using the Ge(IV) source, a phase change material layer was not formed at a temperature less than 300° C. A phase change material layer was also be formed at a temperature less than 300° C., that is, at 280° C. and at 240° C. using the Ge(II) source of Formula 19.

When the reaction gas was H₂, a phase change material layer was formed at a temperature less than 300° C., that is, at 280° C. and at 240° C. using the Ge(II) source of Formula 18. However, the deposition rate of the phase change material layer at 280° C. and 240° C. was relatively low. The same result was obtained when using the Ge(II) source of Formula 19.

FIGS. 7A and 7B are photographic images of a phase change material layer formed according to Experimental Example 2 (NH₃ reaction gas and 280° C. deposition). FIGS. 8A and 8B are photographic images of a phase change material layer formed according to Experimental Example 3 (NH₃ reaction gas and 240° C. deposition). FIGS. 9A and 9B are photographic images of a phase change material layer formed according to Experimental Example 4 (NH₃ reaction gas and 200° C. deposition). Each of the photographic images provides visual confirmation that the phase change material layer conformally covered the side wall of a contact hole without blocking the entrance to the hole and without creating voids within the hole.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 

1. A method of forming a phase change material layer, the method comprising: supplying a reaction gas including the composition of Formula 1 into a reaction chamber; supplying a first source which includes Ge(II) into the reaction chamber; and supplying a second source into the reaction chamber; NR₁R₂R₃  Formula 1 wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) and N(C₂H₅)₂.
 2. The method of claim 1, wherein the reaction gas comprises an NH₂ group.
 3. The method of claim 2, wherein the reaction gas is at least one selected from the group consisting of ammonia, primary amine and hydrazine.
 4. The method of claim 1, wherein the first source comprises at least one selected from the group consisting of an amide ligand, a phosphanido ligand, an alkoxide ligand and a thiolate ligand.
 5. The method of claim 4, wherein the first source includes the composition of at least one of Formulae 2 to 4: R₁R₂X₁—Ge—X₂R₃R₄  Formula 2 wherein X₁ and X₂ are each independently at least one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₅R₆, where R₅ and R₆ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₇R₈R₉, where R₇, R₈ and R₉ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 2 includes non-ring systems and ring systems in which at least two of the R₁, R₂, R₃ and R₄ are chemically linked; R₁Y₁—Ge—Y₂R₂  Formula 3 wherein Y₁ and Y₂ are each independently at least one of O and S, wherein R₁ and R₂ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₃R₄, where R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₅R₆R₇, where R₅, R₆ and R₇ are each independently at least one of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 3 includes non-ring systems and ring systems in which R₁ and R₂ are chemically linked; R₁R₂X—Ge—YR₃  Formula 4 wherein X is at least one of N and P, and Y is at least one of O and S, wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (g) a C₂-C₁₃ acetylenic group, (h) an allenic group (CHCCH₂), (i) a cyano group (CN), (j) a NCX group, where X is O, S, Se or Te, (k) an azide ligand (N₃), (l) an amide ligand (NR₄R₅, where R₄ and R₅ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (m) SiR₆R₇R₈, where R₆, R₇ and R₈ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 4 includes non-ring systems and ring systems in which at least two of R₁, R₂ and R₃ are chemically linked.
 6. The method of claim 4, wherein the first source includes the composition of at least one of Formulae 5 to 11:

wherein X₁ and X₂ are each independently one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉ and R₁₀ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group; and

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.
 7. The method of claim 4, wherein the first source includes the composition of at least one of Formulae 12 to 16:

wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein Y₁, Y₂, Y₃ and Y₄ are each independently one of O and S, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group, and

wherein Y₁, Y₂, Y₃ and Y₄ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.
 8. The method of claim 5, wherein the first source includes the composition of Formula 17:

wherein X is one of N and P, wherein Y is one of O and S, and wherein R₁, R₂ and R₃ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.
 9. The method of claim 1, wherein the second source is at least one source selected from the group consisting of a Te source, a Sb source, a Bi source, an As source, a Sn source, an O source, an Au source, a Pd source, a Se source, a Ti source and a S source.
 10. The method of claim 1, wherein the phase change material layer is one selected from the group consisting of Ge—Sb—Te layer, Ge—Bi—Te layer, Ge—Te—As layer, Ge—Te—Sn layer, Ge—Te layer, Ge—Te—Sn—O layer, Ge—Te—Sn—Au layer, Ge—Te—Sn—Pd layer, Ge—Te—Se layer, Ge—Te—Ti layer, (Ge, Sn)—Sb—Te layer, Ge—Sb—(Se, Te) layer and Ge—Sb—Te—S layer.
 11. The method of claim 1, wherein at least one of the first source and the second source are supplied into the reaction chamber with a carrier gas.
 12. The method of claim 1, wherein the first source and the second source are supplied into the reaction chamber at the same time a carrier gas and the reaction gas are supplied into the reaction chamber.
 13. The method of claim 1, further comprising purging physically adsorbed sources and unreacted sources by supplying a carrier gas and the reaction gas into the reaction chamber after supplying the first source and the second source into the reaction chamber.
 14. A method of forming a phase change material layer, the method comprising: supplying a first source including Ge(II) into a reaction chamber; and supplying a second source into the reaction chamber, wherein the first source comprises at least one selected from the group consisting of an amide ligand, a phosphanido ligand, an alkoxide ligand and a thiolate ligand.
 15. The method of claim 14, wherein the first source includes the composition of at least one of Formulae 2 to 4: R₁R₂X₁—Ge—X₂R₃R₄  Formula 2 wherein X₁ and X₂ are each independently at least one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₅R₆, where R₅ and R₆ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₇R₈R₉, where R₇, R₈ and R₉ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 2 includes non-ring systems and ring systems in which at least two of the R₁, R₂, R₃ and R₄ are chemically linked; R₁Y₁—Ge—Y₂R₂  Formula 3 wherein Y₁ and Y₂ are each independently at least one of O and S, wherein R₁ and R₂ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₃R₄, where R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₅R₆R₇, where R₅, R₆ and R₇ are each independently at least one of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 3 includes non-ring systems and ring systems in which R₁ and R₂ are chemically linked; R₁R₂X—Ge—YR₃  Formula 4 wherein X is at least one of N and P, and Y is at least one of O and S, wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (g) a C₂-C₁₃ acetylenic group, (h) an allenic group (CHCCH₂), (i) a cyano group (CN), (j) a NCX group, where X is O, S, Se or Te, (k) an azide ligand (N₃), (l) an amide ligand (NR₄R₅, where R₄ and R₅ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (m) SiR₆R₇R₈, where R₆, R₇ and R₈ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 4 includes non-ring systems and ring systems in which at least two of R₁, R₂ and R₃ are chemically linked.
 16. A method of forming a phase change material layer, the method comprising: supplying a first source including Ge(II) into a reaction chamber; and supplying a second source into the reaction chamber wherein the first source includes the composition of at least one of Formulae 5 to 17:

wherein X₁ and X₂ are each independently one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₈ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈, R₉ and R₁₀ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁, X₂, X₃ and X₄ are each independently one of N and P, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group; and

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein Y₁, Y₂, Y₃ and Y₄ are each independently one of O and S, and wherein R₁, R₂, R₃, R₄, R₅ and R₆ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X₁ and X₂ are each independently one of N and P, wherein Y₁ and Y₂ are each independently one of O and S, and wherein R₁, R₂, R₃ and R₄ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group, and

wherein Y₁, Y₂, Y₃ and Y₄ are each independently one of O and S, and wherein R₁ and R₂ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group;

wherein X is one of N and P, wherein Y is one of O and S, and wherein R₁, R₂ and R₃ are each independently one selected from the group consisting of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group and an allenic group.
 17. The method of claim 14, wherein the second source is at least one source selected from the group consisting of a Te source, a Sb source, a Bi source, an As source, a Sn source, an O source, an Au source, a Pd source, a Se source, a Ti source and a S source.
 18. A method of fabricating a phase change memory device, the method comprising: loading a substrate comprising a lower electrode in a reaction chamber; forming a Ge-containing phase change material layer on the lower electrode by supplying a reaction gas including the composition of Formula 1, a first source including Ge(II), and a second source into the reaction chamber in which the substrate is loaded; and forming an upper electrode on the phase change material layer; NR₁R₂R₃  Formula 1 wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of H, CH₃, C₂H₅, C₃H₇, C₄H₉, Si(CH₃)₃, NH₂, NH(CH₃), N(CH₃)₂, NH(C₂H₅) and N(C₂H₅)₂.
 19. The method of claim 18, wherein the first source includes the composition of at least one of Formulae 2 to 4: R₁R₂X—Ge—X₂R₃R₄  Formula 2 wherein X₁ and X₂ are each independently at least one of N and P, and wherein R₁, R₂, R₃ and R₄ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₅R₆, where R₅ and R₆ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₇R₈R₉, where R₇, R₈ and R₉ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 2 includes non-ring systems and ring systems in which at least two of the R₁, R₂, R₃ and R₄ are chemically linked; R₁Y₁—Ge—Y₂R₂  Formula 3 wherein Y₁ and Y₂ are each independently at least one of O and S, wherein R₁ and R₂ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (e) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (g) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (h) a C₂-C₁₃ acetylenic group, (i) an allenic group (CHCCH₂), (j) a cyano group (CN), (k) a NCX group, where X is O, S, Se or Te, (l) an azide ligand (N₃), (m) an amide ligand (NR₃R₄, where R₃ and R₄ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (n) SiR₅R₆R₇, where R₅, R₆ and R₇ are each independently at least one of a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 3 includes non-ring systems and ring systems in which R₁ and R₂ are chemically linked; R₁R₂X—Ge—YR₃  Formula 4 wherein X is at least one of N and P, and Y is at least one of O and S, wherein R₁, R₂ and R₃ are each independently at least one selected from the group consisting of (a) a hydrogen atom, (b) a C₁-C₁₀ alkyl group, (c) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, (d) a C₁-C₁₀ alkyl group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (d) a C₂-C₁₂ olefinic group, (f) a C₃-C₁₂ olefinic group, where CH₃ is substituted with an imine group, an amine group, an alkoxy group or a ketone group, and where N of the imine group, N of the amine group, O of the alkoxy group or O of the ketone group is coordinated with Ge, (g) a C₂-C₁₃ acetylenic group, (h) an allenic group (CHCCH₂), (i) a cyano group (CN), (j) a NCX group, where X is O, S, Se or Te, (k) an azide ligand (N₃), (l) an amide ligand (NR₄R₅, where R₄ and R₅ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group), (m) SiR₆R₇R₈, where R₆, R₇ and R₈ are each independently a hydrogen atom, a C₁-C₁₀ alkyl group, a C₂-C₁₂ olefinic group, a C₂-C₁₃ acetylenic group or an allenic group, and wherein the representation of Formula 4 includes non-ring systems and ring systems in which at least two of R₁, R₂ and R₃ are chemically linked. 